Kinnibrugh T, Bhattacharjee S, Sullivan P, Isborn C, Robinson B H, Eichinger B E
Chemistry Department, New Mexico Highlands University, Las Vegas, New Mexico 87701, USA.
J Phys Chem B. 2006 Jul 13;110(27):13512-22. doi: 10.1021/jp0608271.
The influence of rotational and geometrical isomerism on the nonlinear optical (NLO) properties, specifically the first-order hyperpolarizability beta, of chromophores of current interest has been investigated with density functional theory (DFT). In the first of this two-part study, the rotational isomerism of a linear chromophore was explored. Calculation of the torsion potentials about two of the rotatable and conformation-changing single bonds in a chromophore demonstrated the near equality of the molecular energies at 0 degrees and 180 degrees rotational angles. To explore the consequences of this near conformational energy degeneracy to NLO behavior, the eight low energy rotational isomers of FTC [Robinson, B. H.; et al. Chem. Phys. 1999, 245, 35] were investigated. This study provides the first-reported DFT-based calculation of the statistical mechanical average of beta over the conformational space of a molecule having substantial nonlinear optical behavior. The influence of the solvent reaction field on rotameric populations and on the beta tensor is reported. In the second part, two molecules having two donors and two acceptors bonded respectively in ortho and meta positions on a central benzene ring are shown to have substantially different beta tensors. These two so-called molecular Xs have different highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) distributions, and consistent with expectations, it is found that the larger beta(zzz) is associated with a large spatial asymmetry between the HOMOs and LUMOs. Large hyperpolarizability correlates with the HOMO concentrated on the donor groups and the LUMO on the acceptor groups.
利用密度泛函理论（DFT）研究了旋转异构和几何异构对当前感兴趣的发色团的非线性光学（NLO）性质，特别是一阶超极化率β的影响。在这个两部分研究的第一部分中，探讨了线性发色团的旋转异构。对发色团中两个可旋转且能改变构象的单键的扭转势进行计算，结果表明在0°和180°旋转角度下分子能量几乎相等。为了探究这种近乎简并的构象能量对NLO行为的影响，研究了FTC的八种低能量旋转异构体[罗宾逊，B. H.等人，《化学物理》，1999年，第245卷，第35页]。这项研究首次报道了基于DFT对具有显著非线性光学行为的分子构象空间上β的统计力学平均值的计算。报道了溶剂反应场对旋转异构体数量和β张量的影响。在第二部分中，展示了两个分别在中心苯环的邻位和间位键合有两个供体和两个受体的分子具有显著不同的β张量。这两个所谓的分子X具有不同的最高占据分子轨道到最低未占据分子轨道（HOMO - LUMO）分布，并且正如预期的那样，发现较大的β(zzz)与HOMO和LUMO之间较大的空间不对称性相关。大的超极化率与集中在供体基团上的HOMO和受体基团上的LUMO相关。
